Utilization of organic light-semiconductors in electrophotography has heretofore been studied. From German Patent Publication No. 1,068,115 and U.S. Pat. No. 3,037,861, it is known that polyvinyl carbazole is photoconductive and can be used in electrophotographic processes. Furthermore, the German Patent Publication discloses that addition of a small amount of dye increases the photosensitivity of polyvinyl carbazole.
German Patent Publication No. 1,572,347 and U.S. Pat. No. 3,484,237 disclose an electrophotographic recording medium bearing a photoconductive coating film prepared from a photoconductive composition comprising a polymer of a heterocyclic vinyl compound, e.g., polyvinyl carbazole and 0.49 to 1.23 mols of 2,4,7-trinitro-9-fluorenone per mol of the repeating unit of the polymer.
The electrophotographic recording medium as disclosed in German Unexamined Patent Publication (OLS) No. 1,797,561 has an electrophotographic coating film prepared from a photoconductive composition containing equal parts by weight of 2,4,7-trinitro-9-fluorenone and polyvinyl carbazole.
R. M. Schefelt describes in IBM Journal of Research and Development, Vol. 15, No. 1, pages 75 to 89 (1971) that the above-described recording media have excellent properties resulting from charge transfer complexes constituting their photoconductive coating films. Furthermore, the disclosure is that a number of substances which are described as sensitizers for polyvinyl carbazole have low mutual-solubility with polyvinyl carbazole and when used in higher concentrations, these substances adversely influence the photosensitivity (ibid., p. 76) and that none of these substances are as useful as 2,4,7-trinitro-9-fluorenone (ibid., p. 77).
Trinitrofluorenone is a relatively expensive substance and has very high physiological activity.